Chemokine receptor CCR5 is co-receptor for the HIV virus entry to host cells. The application of CCR5 antagonist in blocking the entry may provide a novel anti-HIV therapeutic pathway. Our long-term goal is to develop potential antagonist(s) of chemokine receptor CCR5 as novel anti-HIV agents. The specific hypothesis is that an antagonist of CCR5 with structural character to interact with the extracellular loop II (EL2) of the CCR5 receptor may have therapeutic potency as anti-HIV agents. We base that hypothesis on the following facts: First, in order to initiate the merging of the HIV viral membrane to the host cell membrane, the envelope protein gp120 on HIV virus membrane may have to bind to the extracellular part (including all three extracellular loops and amino terminal) of the receptor to initiate the process. Therefore, EL2 in the receptor is believed to be critical to the entry of the HIV-1 virus. Second, endogenous peptide antagonists and agonists of CCR5 all bind to the receptor on the extracellular part, including EL2 part while non-peptide ligand's binding locus may adopt EL2 part as well. Based on these observations, the experimental focus of this proposal is the synthesis of CCR5 non-peptide antagonists carrying structural features to interact with EL2 of the receptor. The specific aims are to: 1. Design and synthesize novel compounds as CCR5 antagonists based on fully characterization of CCR5 antagonist binding site(s) by molecular modeling. We have finished the CCR5 homology model construction and characterized the antagonist binding site by adopting the model. A series of new ligands has been designed, synthesized and tested as anti-HIV agent and a novel lead compound has been identified. The second round molecular design has been conducted. We will finish the synthesis of the ligands designed for biological evaluation. 2. Evaluate the biological activity of the compounds synthesized as anti-HIV agents to verify our homology model, to identify new lead compound with higher activity and to further test our hypothesis. Biological screening will include: RANTES-binding inhibition assay to test the affinity of ligands to CCR5 receptor, anti- HIV testing in CEM-SS cells with laboratory-derived strains (RF), anti-HIV attachment assays to GHOST CCR5 cells, and Anti-HIV testing in fresh human monocytes-macrophages with CCR5-tropic virus strains. [unreadable] [unreadable] [unreadable]